Electronic devices, including mobile electronic devices, provide an array of features, some within very compact packaging, that make communication, messaging and exchanging of information, including audio and video information, transparent to a user. Many such devices provide ports to expand the functionality of the device or to couple the device to accessories that allow for more convenient operation of, or interaction with, the device. Some electronic devices can provide a bias signal, such as for a microphone of an accessory device. The bias signal can deplete energy from the device, such as from a battery of a mobile electronic device, even when an accessory is not coupled to a port of the device.